1. Field of the Invention
This invention relates to an apparatus for driving a light-emitting display constructed of light-emitting elements such as organic EL elements and light-emitting diodes.
2. Description of the Related Art
Where an image is displayed on the light-emitting display, each light-emitting element must be illuminated with the luminance corresponding to the luminance value of each of pixels of an image signal.
The technique for illuminating each light-emitting element with the luminance corresponding to the luminance value of the pixel includes an analog method and a time-divisional method.
The analog method is to vary the driving current of illuminating the light-emitting element according to the luminance value. The time-divisional method is to turn on/off the driving current, which is maintained constant, according to the luminance value, thereby varying its xe2x80x9cONxe2x80x9d time.
The analog method requires linearity at high accuracy in order to vary the driving current according to the luminance value. Therefore, the analog method has a disadvantage that a driving section is up-sized and the value of the driving current varies according to a temperature.
On the other hand, in the time-divisional method in which requires a constant current to be produced, the driving section is down-sized and has a good temperature characteristic.
Now referring to FIG. 11 an explanation will be given of a driving apparatus in a time-divisional system.
In FIG. 11, reference numeral 50 denotes a frame memory for storing an image signal (pixel data) corresponding to its one frame; 51 a pattern memory; 52 a read section; 53 a driving section for producing a constant driving current; and 54 a light-emitting display.
For simplicity of explanation, the explanation will be made for a single pixel.
The read section 51 reads the pixel data stored in the frame memory in a frame period.
The luminance value of the pixel data is represented by a binary number of k (2k) Specifically, where k=8, the luminance is represented by 256 levels.
The pattern memory 51 stores schedule data (pattern information) for turning on the driving section 53 for the pixel data read by the read section 50.
FIG. 12 shows a concrete example of the contents of the pattern memory 51 where k=3.
The addresses of the pattern memory 51 are correlated with the pixel data read from the frame memory 50. The pattern information is recorded as the bit information of 2kxe2x88x921.
Namely, where k=3, the address is represented by 3 bits and the pattern information is represented by 7 bits.
For example, as seen from FIG. 12, where the address is xe2x80x98000xe2x80x99, the pattern information is xe2x80x980000000xe2x80x99, and where the address is xe2x80x98001xe2x80x99, the pattern information is xe2x80x981000000xe2x80x99. Likewise, the pattern information will be previously stored as seen from FIG. 12.
Using the addresses of the pixel data read from the frame memory 50, the read section 52 reads the pattern information stored in the pattern memory 51 and sequentially sends it to the driving unit 53 in a period of 1/(2kxe2x88x921) of the frame period.
Where the signal sent from the read section 52 is xe2x80x9c1xe2x80x9d, the driving section 53 supplies a constant current to the light-emitting display 54, whereas the signal sent from the read section 52 is xe2x80x9c0xe2x80x9d, the driving section 53 stops supply of the current.
Generally, the image data has the luminance values of 8 bits or larger, i.e. 2kxe2x88x921=255 level or larger. In this case, the pattern memory requires 256 addresses and memory capacity of 255 bits.
In the conventional apparatus for driving a light-emitting display in a time-divisional manner, where the image signal is represented by a binary number of k, the driving section 53 is on/off controlled in a period of 1/(2kxe2x88x921) of the frame period, thereby requiring a high speed operation.
An object of this invention is to provide an apparatus for driving a light-emitting display which drives a driving section at a driving rate lower than e.g. (2kxe2x88x921)f and equivalently provides the number of levels corresponding to 2K in a frequency band lower than fF/2 which is a reproduction band of a moving image, i.e. Nyquist band.
In order to the above object, in accordance with an aspect of this invention, there is provided a driving apparatus for a light-emitting display which controls the light-emission of M number of light-emitting elements in such a manner that a driving current or driving voltage is turned on or off by an on/off signal supplied through a driving unit, comprising:
a pixel read section for reading the luminance values for the light-emitting elements in a frame period from an image signal; and
a xcex94xcexa3 modulator which operates in a sub-frame period which is 1/n of the frame period according to the luminance values read by the pixel read section, wherein an output of xe2x80x9c1xe2x80x9d or xe2x80x9c0xe2x80x9d from xcex94xcexa3 modulator is supplied to the driving unit as the on/off signal.
In this configuration, the luminance value of the pixel is subjected to the xcex94xcexa3 modulation, and the driving current or the driving voltage is turned on/off using the output from the xcex94xcexa3 modulator. For this reason, even if the on/off frequency of the driving current or driving voltage is lowered, a necessary S/N ratio can be assured within a reproduction frequency band of an image.
In order to the above object, in accordance with another aspect of this invention, there is provided a driving apparatus for a light-emitting display which controls the light-emission of M number of light-emitting elements in such a manner that a driving current or driving voltage is turned on or off by an on/off signal supplied through a driving unit, comprising:
a pixel read section for reading the luminance values of the light-emitting elements in a frame period from an image signal;
a xcex94xcexa3 modulator which operates in a sub-frame period which is 1/n of the frame period according to the luminance values read by the pixel read section; and
a random data generator for generating random luminance values of individual pixels,
wherein in an image displaying operation, the output from the random data generator is directly supplied to the xcex94xcexa3 modulator in place of the output from the pixel read section, or otherwise added to the output from the pixel read section.
Where the random luminance values are supplied to the xcex94xcexa3 modulator when the driving apparatus is started, the blinking of the display can be prevented.
The above and other objects and features of this invention will be more apparent from the following description taken in conjunction with the accompanying drawings.